This application claims the priority of German patent document 196 44 879.4, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and apparatus for signalling theft for a motor vehicle, in which an item of theft-signalling information is produced as a function of the signal state of at least one of a plurality of signals which are output by corresponding vehicle-state monitoring means.
As used herein, theft is to be understood as including not only to unauthorized taking of the vehicle, but also an unauthorized attempt to enter the vehicle. The term vehicle-state monitoring means refers to the components on the vehicle which output signals that supply information on the current state of the vehicle. These include in particular sensors for detecting unauthorized tampering with an unauthorized access protection device (for example a central locking system), and/or an unauthorized use protection device (for example an electronic immobilizer), and vehicle components which produce signals relating to the operation of the vehicle, such as an ignition line signal, a fuel pump signal, signals from wheel rpm sensors etc.
Methods and devices of this kind are customary in a variety of forms for modern motor vehicles. The theft-signalling information produced when an attempted theft is detected usually triggers an alarm system arranged on the vehicle. There are also systems already known in which the theft-signalling information is transmitted (preferably in addition to triggering an alarm signal on the vehicle) via a wireless signal transmission link to a monitoring point outside the vehicle, in order to initiate suitable measures against the attempted theft from said point. For example, an electronic immobilizer and/or pursuit of a vehicle by means of an appropriate locating system, may be triggered. Such systems are disclosed, for example, in German patent documents DE 39 26 983 A1, DE 42 03 865 A1, EP 0 388 756 A2 and WO 93/24911 as well as the patent documents EP 0 366 378 B1 and DE 42 43 415 C1. In addition, these publications describe various vehicle-state monitoring means, of which preferably a plurality are provided in each case, in order to monitor the vehicle both in terms of attempted break-ins and in terms of attempts at driving it away and/or transporting it away.
In all the systems described in these publications, the theft-signalling information is produced if the signals which are indicative of vehicle states indicate an attempted theft, for example an attempt at break-in, an attempt at driving away or an attempt at transporting away. In such cases, the theft-signalling information triggers the vehicle alarm, and is simultaneously passed on via the wireless transmission link to the remote monitoring point. The malfunction of one of the vehicle-state monitoring means, which leads to incorrect production of the theft-detecting signal state for the respective signal, thus undesirably results in the monitoring point incorrectly concluding that a theft is occurring and initiating the appropriate countermeasures. There is therefore need for improvement of the reliability of the theft-detection means.
In a theft alarm system described in the European patent document EP 0 641 693 A1, selective activation and deactivation of various system components is possible. In addition, specific time delays are provided for the transmission of sensor signals relating to theft, in order to facilitate the transmission of data over a combined transmission channel without data collisions and to be able to perform operations, in the time periods thus provided, for proving an authorized vehicle access or an authorized vehicle use. Such time periods for proving the use authorization are also provided with a method for releasing an activated electronic immobilizer, which method is described in patent DE 44 16 118 C1.
The object of the present invention is to provide a method and apparatus of the type mentioned above, which makes it possible to signal thefts in a way which is comparatively protected against incorrect alarms, in particular, when necessary, also for signalling theft to a monitoring point which is arranged spatially remote from the vehicle.
This object is achieved by the method and apparatus according to the invention, in which theft-signalling information is produced only if the signal states of a plurality of signals which are indicative of vehicle states are present in one of one or more prescribed theft-signalling combinations. Each such theft-signalling combination comprises one or more signalling conditions, which succeed one another in a specific time sequence and which themselves comprise one or more combinations, which are indicative of theft, of jointly interrogated signal states of the signals which are indicative of vehicle states.
In this way, a theft is signalled only when the appropriate signal states of a plurality of signals which are indicative of theft occur in a correct simultaneous combination and/or in a correct time sequence. If only one signal which is indicative of a vehicle state assumes its signal state which is indicative of theft, this does not lead to a theft being signalled, and the system in question is consequently failsafe with respect to single faults. In addition, multiple faults do not necessarily lead to a theft being incorrectly signalled; rather only in the highly improbable case in which, as a result, one of the prescribed theft-signalling combinations is randomly produced. In addition, since the simultaneous occurrence of a plurality of signal faults is itself relatively improbable, the result is that the method and device according to the invention permit very reliable, failsafe signalling of thefts.
One embodiment of the invention makes it possible to signal a theft situation in which, after towing away or entering the vehicle without authorization, an attempt is being made to activate said vehicle without authorization by bypassing an electronic immobilizer by replacing at least one control unit (for example the engine control unit) which relates to the operation of the vehicle with an external control unit.
Another embodiment of the invention is particularly suitable for detecting a theft situation in which an unauthorized attempt is being made t6 appropriate the vehicle by loading it onto another vehicle and transporting it away. Similarly, still another embodiment is particularly suitable for detecting an unauthorized attempt is to appropriate the vehicle by towing it away.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.